JPS6150119A - Drive circuit for liquid crystal display device - Google Patents

Abstract

PURPOSE:To raise the minimum driving frequency of a liquid crystal to prevent the variance of display by providing an exclusive OR circuit to which an output signal obtained by dividing the frequency of a latch signal and counting this divided signal and a liquid crystal driving waveform AC signal outputted from a control circuit are inputted. CONSTITUTION:The control circuit 2 controls the operation of a liquid crystal module 1. Segments-side driving circuits 4a and 4b output signal voltages to signal lines Y1-Yn of a liquid crystal panel 3, and a scan-side driving circuit 5 outputs selecting pulses to scan scanning lines X1-Xn of the panel 3 successively. A liquid crystal power supply driving circuit 6 supplies voltages which drive circuits 4a and 4b by the voltage averaging method, and turn-on/off information signals of all picture elements are inputted to terminals D1 and D2. A counter circuit 10 which counts a latch signal CL1 from a timing generating circuit 7 and an exclusive OR circuit 11 to which the output of the circuit 10 and a liquid crystal driving waveform AC signal M are inputted are provided between the module 1 and the circuit 2, and the minimum driving frequency is raised to prevent the variance of display.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a drive circuit for a liquid crystal display device, and particularly to a drive circuit suitable for preventing the occurrence of display unevenness caused by large fluctuations in the threshold voltage of a liquid crystal on the low frequency side. This invention relates to a liquid crystal drive circuit.

[Background of the invention]

When driving a liquid crystal display element in a time-division manner, a voltage averaging method is generally used, which involves reversing the polarity within one frame time (the time for one full scan). There are two types: one that converts to alternating current (hereinafter referred to as method A) and one that converts to alternating current by reversing the polarity in 2 frame time (hereinafter referred to as method B).
There are different methods. These drive systems are discussed in detail, for example, in the August 16, 1980 issue of Nikkei Electronics, pages 150 to 174.

The time-division driving method for liquid crystal display elements is described in the above-mentioned literature, but the B-method driving is currently being used as the mainstream as the number of time divisions increases in order to reduce the burden on the driver LSI. ing.

However, the lowest g motion frequency in the B-method drive is half the frame frequency, and there are cases where f'L is driven at an extremely low frequency. -10,000,'l'd- product's r, 1-value voltage has frequency dependence, and if the 170 voltage of this liquid crystal fluctuates greatly on the low frequency side, use the B method and drive described above. In this case, it has become clear that poor display unevenness appears depending on the lighting pattern.

For example, as shown in FIG. 1, if the liquid crystal has a q characteristic in which the open-direction voltage vth decreases on the low frequency side, as shown in FIG. and scanning electrode Rt
, Rz −R= ? When a voltage is selectively applied between
.

80 The shaded area is Bl, the lighting tone of the f3s part) D
Although the display color is lighter than 131. The display state is darker than the non-lit dots E in the Ba portion, and is colored pale black just like the shape. This is Al lA! Since the frequency component of the driving voltage applied to the liquid crystal of the line in the JA8 section is significantly lower than the frequency component of the driving voltage applied to the liquid crystal on the line of the Bl and B2 sections, the Considering the frequency characteristics of the voltage, and considering the voltage as a standard, it means that a bidynamic voltage that is qualitatively larger than the Bl+132 part is applied to the Al1A21A3 part, and Al, A, , All Vr'L is Bt, B
I thought more than the unlit dots for ziJ〈lit 1. Display unevenness phenomenon occurs. That is, in FIG. 1, the potential difference vl, vi between the driving voltage Vo applied to the liquid crystal and the threshold voltage at that frequency is 1) Vz, and the Al) An # As portion has B1. This means that a substantially larger W and dynamic voltage is applied than the B portion, and the A1°A a + A6 portion lights up blacker than the Bl and Ba portions. - For example, the pixel al shown in FIG.

al l a8. [
The t'b waveforms are shown in Fig. 3) to (j). In the same figure, when comparing the rE dynamic voltage waveforms applied to the iii'ii element a2 and the remaining pixels a1+aa+a4, it is clear that the frequency components of the drive waveform applied to the pixel a2 are different from those of the other pixels al.
It can be seen that the frequency component is much higher than the frequency component of the E-dynamic type applied to +a8+a4. It is easy to understand from the relationship shown in FIG. 1 that as the difference in the frequency components of the drive waveforms increases, the occurrence of display unevenness increases. Therefore, when comparing the B1 part and the Ba part shown in FIG. 2, since the frequency component of the B1 part is high,
This is supported by the fact that the '81 part appears to be whiter and more transparent.

A possible solution to this problem is to use the A-type drive described above, but it is known that the A1-type drive causes another level of display unevenness.

[Purpose of the invention]

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and its purpose is to
] 1. It is an object of the present invention to provide a drive circuit for a liquid crystal display device that prevents the occurrence of unevenness in the display caused by a drop in direct voltage at low frequencies.

[Summary of the invention]

In order to achieve the above objects, the present invention provides liquid crystals with
The lowest driving frequency when driving by method driving is increased.

[Example of invention]

Next, the details of the present invention will be explained in detail with reference to the drawings.

FIG. 4 is a block diagram of a liquid crystal module for providing an example of a drive circuit for a liquid crystal display device according to the present invention. In the figure, numeral 1 denotes a liquid crystal module consisting of a liquid crystal panel in which multiple liquid crystal pixels are arranged in a matrix and its liquid crystal three-channel circuit, and numeral 1-12 denotes a controller circuit for controlling the operation of liquid crystal module 1. , the liquid crystal panel shown in Figure 3, 712, 4a and 4b are the signal lines Y@ direction of the liquid crystal panel 3 Y l, Y x + Y3...Yn
5 is the scanning line Xi Hx2H in the X4/111 direction of the liquid crystal panel 3.
6 is a segment side drive circuit 4. ．． 4b and scanning side ph circuit 5 using voltage averaging method! ! y, a power supply circuit for operating the liquid crystal 8, which supplies a predetermined voltage for operating the liquid crystal module 1; 7, a latch signal CL1 as a timing signal for operating the liquid crystal module 1; a data shift signal CL2; 8 is a circuit that maintains a predetermined voltage to the liquid crystal driving power supply circuit 6, DIrDt is a signal electric fence yl, Y2
, . . . This is a data terminal for serially inputting ON/OFF information of all pixels on Yll, fF and a frame frequency signal.

In addition, FIGS. 5(a) to 5(d) show the timing of output signals of the controller circuit 2 shown in FIG. 4 in the B-method drive.

In this r/T configuration, the on-off information signal for all images on a certain scanning center is serially input to the data terminals DI and Da. The shift register in the segment side drive circuit 4ap4b receives the data shift signal CTJ! The data is shifted by K. Then, when the serial data is full in the shift register, the launch signal CL
, is output and latched into the latch circuit. Latch data switches analog multiplexer, selects,
It is possible to output a non-selective pulse and light up any dot. In this case, the launch signal CLl is generated every time the frame period τF is divided by the time division number N, and data is latched. In addition, in this B method driving, as mentioned above, the polarity of the liquid crystal drive waveform is reversed within two frames to make it completely AC, and the AC conversion signal M having a period twice the frame period τ is used to perform complete AC for two frames. ing. When all dots are turned on or off using this driving method, the frequency of one chewing waveform applied to the liquid crystal is the frame frequency m2 fp == 1 /τ
The frequency is approximately half that of 7. In this manner, the lowest frequency of the B-method drive becomes low, which causes display unevenness. Therefore, the present invention counts latch signals CL between the liquid crystal module 1 and the controller circuit 2, as shown in FIG. 6 for a first embodiment and FIG. 8 for a second embodiment. A counter circuit 1G outputs - to a new alternating current signal, and an Excl circuit further outputs a new alternating current signal r4 using this alternating current signal M and the original alternating current signal M output from the controller circuit 2.
sive OR circuit 11 (Here, the new alternating current signal M obtained by dividing the frequency of CLl is set to count 16 CLI in this embodiment, and M is the sum of this counter output and the controller output. The output signal is obtained by exclusive ORing with the original M6) Figures 7(a) to (e) show the CL of the first embodiment.
1 r f M +Δ'f, M, M The timing of each number 0 is shown, and Figures 9 (b) to (e) show the timing of each signal in the second embodiment. According to such a ζ4 configuration, the lowest drive frequency can be set higher than the lowest drive frequency in the conventional B method drive, and this is caused by the drop in the open chain voltage vth of the liquid crystal on the low frequency side. Display unevenness can be improved.

FIGS. 10(a) to 10) show the scanning side voltage R1 and signal f! when all dots of the liquid crystal panel shown in FIG. 2 are lit. I voltage Ci
, the drive waveform is set to A method drive, B method drive, and
This figure shows a comparison with the drive according to the T embodiment.
a) # (b) is A method drive, same figure (+ri, (d
) is B method drive Q, same [ff1(e), (f),
(P) is 77 when driven using the first embodiment.
%J waveform is shown. As is clear from the figure, the 5 drive frequency can be set lower than the A method drive and higher than the B Manshiki 411, so that the above-mentioned display unevenness can be improved. 1(a) - (The circles indicate scanning ab when all dots of the liquid crystal panel shown in Fig. 2 are lit.
Each S dynamic type of a pressure R1t 4H side voltage c1 is shown in comparison with A method driving, B method wind wave, and driving according to the second embodiment. is driven by the A method, (e) and (d) are driven by the B method, and (
e) , (f) , (f> indicates the drive waveform when driven by the second embodiment. As is clear from the figure, ?fA dynamic frequency is lower than the A method drive, and the B method drive Since this embodiment can be set higher than the above, the above-mentioned display unevenness can be improved even if this embodiment is used.

Further, the drive circuit according to the present invention shown in FIGS. 6 and 8 is a simple circuit in which only two 0MO8's are added to the conventional circuit, and there is no significant increase in cost.

Moreover, when this drive circuit is viewed from the outside as a black box, it is equivalent to the conventional nine circuits, and the system compatibility is also good.

In the above-described embodiment, the frequency of the latch signal CL is divided by a binary counter, but this is not limited to a 112-decimal counter.

[Effect of rJJ]

As explained above, according to the present invention, it is possible to reduce the minimum driving frequency for driving the liquid crystal, thereby reliably preventing the occurrence of display unevenness, and improving quality and reliability of the liquid crystal display device. It has the extremely unique effect of reducing the number of times you get it.

Brief explanation of the drawings Fig. 1 shows the frequency dependence of the open-direction voltage, and Fig. 2 shows the display unevenness that occurs when the A lamp pattern of Alphabella) E is displayed on the liquid crystal panel. Diagram explaining the occurrence, 3rd
(J) is an operation timing diagram of FIG. 2, FIG. 4 is a block diagram of a liquid crystal module for explaining an example of the activation circuit for a liquid crystal display device according to the present invention, and FIGS. (
d) is an operation timing diagram of FIG. 4, FIG. 6 is a circuit diagram showing one of the liquid crystal drive circuits 51J connected to FIG. 4, and FIGS. 7(a) to (e) are operation timings of FIG. 6. Similar to FIG. 6, FIG. 8 is a circuit diagram showing an example of the liquid crystal drive circuit connected to FIG. a) to (1) are voltage waveform diagrams showing the difference in driving frequency between each driving method of the A method 1 downward movement, the B method driving, and the first embodiment when all dots of the liquid crystal spring N are lit; Figures 11 (a) to (9), like the previous figure, show the difference in L and R image frequencies due to the A method drive, B sword type attachment, and each claw σ1υ method of the second embodiment when all dots of the liquid crystal panel are lit. This is a voltage waveform diagram showing .

1-@・Fist liquid crystal module, 211e dispute controller circuit, 3・Q・・LCD panel, 4a, 4b・・e segment Tsukuda 11 also has a control circuit, 5・・・scanning (;ltj drive circuit, 6. Power supply circuit for driving liquid crystal, 7. φ timing generation circuit, 8. Φ. Power supply circuit, 10. Write counter circuit, 11. --EXclustve-OR circuit.

Agent: Patent Attorney Akio Takahashi Figure 1 Circle number f (Hz) Figure 2 Figure 6 Figure 7 (e) M” Figure 8 fc)M (d)M’ (e) M’″ Figure 10 1st poison diagram

Claims (1)

[Claims] A liquid crystal module comprising a segment-side drive circuit and a scan-side drive circuit that output drive signals to signal electrodes and scan electrodes of a liquid crystal panel in which liquid crystal pixels are arranged in a matrix through signal lines and scan lines, respectively; and the liquid crystal module. A drive circuit for a liquid crystal display device comprising at least a control circuit for controlling an operation of a liquid crystal display device, wherein a counter circuit is provided between the control circuit and the liquid crystal module to divide and count a latch signal output from the control circuit. and an exclusive circuit which receives as inputs a counter output signal outputted from the counter circuit and a liquid crystal drive waveform alternating signal M outputted from the control circuit.
A shive-OR circuit is provided to form an alternating current signal M'' having a higher frequency than the alternating signal M, and this alternating signal M''
A drive circuit for a liquid crystal display device, characterized in that the liquid crystal drive waveform is changed to an alternating current.